The present invention relates to the remote measuring of oceanic (and near surface atmospheric) data under the control of a teleoperator or data acquisition center. More particularly, the invention concerns an autonomous, generally free drifting, data acquisition instrument for extended collection of environmental data from an ocean or fresh water body.
The physical, biological and geological properties of the world's oceans and large fresh water bodies are severely undersampled in time and space. At present, only limited short-term data sets of small portions of such bodies are available. This lack of comprehensive oceanographic information is directly attributable to the high cost of data acquisition. Historically, data collection has been completed using instruments lowered from ships, or moored instrument arrays which must be recovered. The cost of operating a manned vessel on the high seas is prohibitive. Moreover, vessel availability cannot always be assured. Oceanographic experiments are thus constrained in many cases by factors other than the phenomenon which is intended for study.
In light of the foregoing, it is apparent that a lower cost per data point could be attained if the data acquisition process relied less on traditional ship based measurement techniques. To date, there have been various proposals of data acquisition devices which obtain environmental data without the need for a manned vessel to place the device or acquire data therefrom. However, there have been no proposals for a completely autonomous data acquisition instrument capable of: (1) cyclically profiling environmental data over a range of depths, (2) acquiring geographic positions, (3) conducting two way communications, and (4) collecting additional energy over extended periods of time.
With current systems, data collection and distribution is limited by telemetry and power systems, which reduce the amount of data collected and the life of the instrument. There is no provision for bi-directional communications and locating capability, and these instruments must therefore be preprogrammed or moored at fixed locations for later retrieval, all at increased expense. Duda, et al., "The Cartesian Diver: A Self-Profiling Lagrangian Velocity Recorder", Jour. of Atmos. and Ocean. Tech., Vol. 5, No. 1 (Feb 1988), describes a device to vertically profile several parameters. The data are stored in the device for later retrieval. There is no provision for determining location.
Rossby, et al., "The RAFOS System", Jour. of Atmos. and Ocean. Tech., Vol. 3, No. 4 (Dec 1986), describes a subsurface free drifting device (RAFOS) which uses acoustic (experiment specific) tracking methods for determining location of the unit from a remote site (the device has no self-locating capability). Data is communicated using the ARGOS satellite system. Only a small amount of data is stored in RAFOS and the ARGOS satellite data transmission occurs only at the end of a drifting period. The ARGOS system is transmit only, and limited to approximately 256 bits/10 minute satellite pass with a maximum of thirty passes per day at the earth's poles and as low as six passes at the equator. It is significant that an ARGOS based instrument such as RAFOS does not know where it is and hence cannot make a decision based on position. The lack of instrument knowledge of position adds to the uncertainty of when a polar orbiting satellite will be available for data transmission. This uncertainty requires a high level of redundant data transmission and thus increases the amount of energy needed per bit of useful data.
Davis et al (Scripps Institute of Oceanography) have constructed a Lagrangian drifter (ALACE) similar to RAFOS also using ARGOS for data telemetry as well as location determination (from a remote site).
None of the foregoing systems include energy collection, global positioning capability (GPS) or global bi-directional telecommunications. Accordingly, persons skilled the art will recognize that there remains a compelling need for an autonomous controllable, oceanographic data sampling system capable of long term, free ranging movement through oceans and large fresh water bodies.